Sense of school belonging is a crucial factor for healthy development among adolescents. Thus, it is important to understand the factors that might contribute to adolescents’ sense of belonging at school. The primary goals of the present study were to understand the extent to which the quality of a fundamental relationship in the class (i.e., peer acceptance, and supportive and fair relationships with teachers) contributed to the sense of school belonging among early adolescents, and to investigate whether student-teacher relationships can mitigate the detrimental effect of low peer acceptance on adolescents’ sense of school belonging. Data were collected from 7th grade students (N = 1065; Mage = 13.21; SD = .41, 56% males) from 16 upper secondary schools across 4 medium size cities in Sweden. The result of this study showed that, indeed, both peer acceptance and teacher relationship significantly predict the sense of class belonging. However, teacher relationships did not significantly moderate the relation between peer acceptance and class belonging. The findings highlight the importance of relationships within the school context for adolescents’ sense of class belonging. Furthermore, the findings suggest that having a supportive relationship with teachers cannot compensate for the effects of having low peer acceptance on adolescents’ sense of class belonging.